The invention relates generally to the detection of objects located behind an obscuring surface, and more particularly, to a device and method that measures capacitance and based on the capacitance measurements, simultaneously detects and displays images of obscured objects.
Often in the fields of building construction, renovation, and repair, as well as for other purposes, it would be desirable to be able to view an image of objects located behind an obscuring surface, such as a wall. Generating an “X-Ray” type of a view of walls, floors, ceilings, and other obscuring surfaces to find the exact locations of any structural or facilities members hidden behind them would be a significant benefit. In many cases for safety purposes, it is essential to locate any pipes or wires before any penetration of an obscuring surface occurs. In other cases, there is a need to find the exact location of a stud or other bracing member behind the obscuring wall surface for use as a strong support for mounting a heavy object to the wall, such as a mirror. The mounting screw or screws of the object to be hung must penetrate not only the wallboard, but also must extend into the stud since wallboard by itself is typically not strong enough to hold up heavy objects.
One option to determine what exists behind an obscuring wall is to remove the obscuring wall or a part of it. This can be expensive and time consuming. Carpenters for instance, would vastly benefit from the ability to plan improvements by viewing what is behind an obscuring wall without the need for opening that wall. Such wall openings cause an even greater amount of work due to the required repair, closing, and patching of those walls. Electricians and plumbers would also benefit from the ability to determine the exact locations of various obstructions and clear areas behind obscuring wall surfaces so that they could more easily plan their wire or pipe runs. Being able to determine the existence of pipes, wires, conduits, studs, bracing members, and other features would make projects easier, more efficient, and in many cases, less expensive.
Home inspectors would like to be able to determine whether various contractors and homeowners have done their work according to applicable construction codes and whether the materials and fabrication techniques are according to applicable requirements. In most cases, construction inspections are required before an obscuring surface is erected. However, cases have arisen, due to timing or other events beyond the control of those involved, where an obscuring surface is put in place before the required inspection could be performed. In such a case, verifying that proper construction techniques were used may require removal of the wall or other obscuring surface, or at least opening access ports through the wall to allow visual inspections. This leads to the additional time and expense to close the (often multiple) access ports of the wall. Because existing devices and methods do not adequately permit an inspector to check construction materials and techniques that are hidden from view behind an obscuring wall, removal of the wall is the only option in some cases. However, if a device and method were provided that would give the inspector a clearer view of the hidden object or construction techniques, such a device and method may enable an inspector to approve the completed construction without requiring that the wall be removed.
Being able to obtain a display of what is located behind a wall, floor, or ceiling surface is desirable for various purposes, such as locating cavities in floor surfaces, joists, and other areas, determining where fasteners should go when assembling any type of non-conductive structures, locating studs behind plastic, or glass walls, and locating live or non-live wires. Other situations would also benefit from a detector or scanner that can provide an image of the structure or features behind an obscuring surface. For example, it is desirable to be able to scan for hidden wall cavities in buildings, scan for hidden compartments in airplane internal cabin structures, analyze non-ferrous boat hulls to find hidden contraband cavities and/or metal sub-structures, locate hidden items in suitcases, and locate contraband at schools and in other places.
Various technologies have been proposed to avoid having to open an obscuring wall to find objects located behind that wall. These range from a simple metal detector comprising a pivoting magnet, to more complex metal detectors (see U.S. Pat. No. 4,853,617), to capacitive sensor systems, to a short-range radar system (see U.S. Pat. No. 5,774,091). A simple “stud finder” has been available for many years that is often used in an attempt to find the vertical support studs of a wall. Such stud finders detect ferrous metals using a compass-like pivoting magnet. The magnet was often pivoted at its middle and had a rest position that would be parallel to an obscuring surface against which the housing of the detector was applied. A portion of the case in which the pivoting magnet was mounted was clear so that pivoting movement of the magnet could be seen. This stud finder was much more effective in commercial buildings were metal studs are used. In the typical home setting, the magnetic stud finder would only work with wooden studs by locating the metal nails used to mount the wallboard or wooden lath, or a ferrous nail used to attach a stud to the bottom plate of the wall. When the detector was moved along the wallboard, the magnet would pivot and point to a ferrous material in the wall. However this detector does not locate a wooden stud per se, it only locates a ferrous nail that may or may not be in the stud. It also does not provide a clear display of the nail it locates. The only display is that the magnet points in the direction of the nail. As the detector is moved across the wallboard that is obscuring sight of the nail, the magnet will continue to angle itself towards the nail, until its sensitivity is exceeded. The magnet then returns to it rest position. This device has minimal usefulness in a wood frame structure.
Perhaps the most successful technology used in detecting objects located behind concealing surfaces is the capacitive sensor/detector. This sensor works by detecting density changes in a wall and is therefore not limited to detecting only ferrous materials. The capacitive sensor can detect non-electrically conductive materials also. These capacitive finders can typically detect changes in wall density to a thickness of about three-quarters of an inch (19 mm). More advanced models have increased sensitivity to approximately a little more than an inch (26 mm). This detector does not work as well with thicker walls and does not provide a clear display of other objects behind the wall, such as pipes and wiring that are located more than approximately one inch (26 mm) away. Before driving a nail into a wallboard, it is important to know that the object obscured by the wallboard at that position is really a stud and is not a pipe.
Capacitive detector devices and methods have been provided with many different circuits used to implement them. There are, however, drawbacks to such devices one of which is that they are incremental in nature and the display they provide is not as desirable as many would want. They are referred to as being “incremental” because they use discrete capacitive components that are able to provide a detection area that is only as large as the capacitive component itself. Adding additional capacitive components has been attempted (see, for example, U.S. Pat. No. 6,198,271 to Heger et al.) but the cost and circuit complexity also undesirably increase. Providing greater and greater numbers of discrete capacitive detector devices or arrays of detectors in a single housing would cause the need for more wiring, more circuits, and more displays or display elements, all of which can increase the cost and size of a detector significantly.
Manual scans using a capacitive handheld device can take time to clearly locate a hidden stud. Furthermore, even when the device detects and displays a hidden object in the wall, the displayed shape does not visually persist as the device is moved along the wall toward or away from the hidden object. No real image of the entire object is provided, only incremental images of parts of the object are provided as the detector is moved along the obscuring surface. The viewer must then assemble these parts in his or her mind to “visualize” the entire object that is obscured. Thus another drawback in capacitive detector devices is the lack of persistence of the detected shape of a hidden object behind an obscuring surface.
U.S. Pat. Nos. 7,982,450 and 8,638,086 to Smoot describe devices and methods to provide an image of objects behind an obscuring, non-conducting surface using a capacitive detection approach. The disclosed devices and methods have provided a significant advance in the art and have solved a long-standing need for contractors, construction workers, and homeowners to be able to accurately visualize objects (studs, pipes, electrical wiring, etc.) behind obscuring wall surfaces. Yet further needs have been identified for providing a higher persistence of image, greater sensitivity of the detector, and for more economically providing a detector.
In regard to sensitivity, another factor in providing a successful detection and display device is the ability to penetrate far enough through the obscuring surface to detect and display as much as possible behind that surface; i.e., a device having increased sensitivity. Some walls are thicker than other walls. For example, walls constructed of lath and plaster are typically much thicker than the walls constructed of standard drywall materials. A lath and plaster wall may be 1.125″ thick (2.86 cm) while a wall formed of wallboard may only be 0.5″ thick (1.3 cm). Wallboard can vary from ½″ (1.27 cm) to ⅝″ (1.59 cm) depending on the type used.
Also, various building techniques can result in thicker walls. For example, soundproofing techniques can make the surface layer of a wall much thicker. In another soundproofing technique, a double wall is provided. In these cases, the pipes and electrical wiring are located even farther within the wall from the wall's surface. In such cases, the sensitivity of the detector would need to be higher in order to detect non-conductive objects located within such walls.
Hence, those skilled in the art have recognized a need for a capacitive detector device and method having a higher sensitivity for detecting objects located behind an obscuring surface, and to display an image of what is detected with a larger display area. A further need has been recognized for a capacitive detector device that provides an image of objects detected behind an obscuring surface, that image having a higher persistence level so that a more accurate picture of the detected objects may be visualized. Yet a further need has been recognized to more economically provide such a detector and display device. The invention satisfies these needs and others.